This invention relates to narrow width molded case circuit breakers and more particularly to a line, or supply, side electrical connection between the circuit breaker and a supply conductor of a panel to which the circuit breaker is mounted.
A circuit breaker of the type to which this invention relates is described and claimed in U.S. Pat. No. 4,430,631 issued to Kenneth A. Forsell et al, Feb. 7, 1984, and assigned to the assignee of this invention, which patent is incorporated herein by reference. The circuit breaker comprises a molded case which supports a line side terminal to which a stationary contact is affixed and a load side terminal to which a bimetallic element of a trip assembly is affixed. An operator handle is pivotally supported in the case to project externally through a forward, or upper wall. A conductive arm which has a movable contact affixed thereto is pivotally supported from the handle. An over center spring is connected to the movable contact conductive arm and to a pivoted latch lever to effect either automatic separation of the contacts by the latch lever and trip assembly or selective manual closing or separation of the contacts by movement of the operator handle.
A current path exists through the circuit breaker from the line side terminal, through the stationary and movable contacts, the conductive arm, a flexible braided conductor connected between the conductive arm at one end and the bimetal element at its opposite end, through the bimetal element to the load side terminal. Overload currents of a first predetermined magnitude flowing through the circuit breaker heat the bimetal element, causing it to deflect away from the latch lever, releasing the lever and causing the spring to move over center and effect separation of the contacts. Overload currents of a second predetermined magnitude, greater than the first, generate an electromagnetic field about the bimetal element, which field attracts an armature, causing it to move away from and release the latch lever for contact separation as described hereninabove. A third predetermined level of overload current, higher than each of the previously mentioned levels, causes contact separation in a current limiting mode. The stationary contact is affixed to the lower end of a straight internal portion of the line side terminal. The movable contact conductive arm is disposed within the case in close parallel proximity, coextensive with the straight portion of the line side terminal when the stationary and movable contacts are engaged. The current path in the line side terminal and the conductive arm are oppositely directed and therefore generate repelling electromagnetic forces, causing the movable contact conductive arm to move away from the line side terminal and stationary contact upon the occurrence of high fault current conditions, such movement occurring independently of the operating mechanism or the latch mechanism.
In circuit breakers such as that disclosed in U.S. Pat. No. 4,430,631, the line side terminal is essentially an inverted U-shaped member with an exiting leg extending downwardly within the casing parallel to the straight portion on which the stationary contact i mounted and exits the casing at a lower corner. The external portion of the terminal is provided with a captive nut for bolted connection to a supply bus conductor. The material thickness and irregular structural formation of the exiting portion of the line side terminal portion establishes an electrical resistance which creates a significant voltage drop and tends to generate heat in addition to heat that is already generated within the current carrying parts of the circuit breaker. Moreover, the general direction of the current path within this exiting portion of the line side terminal is opposite and parallel to the current path in the straight portion to which the stationary contact is affixed. Thus current flow in the exiting portion creates an electromagnetic field which, due to its proximity to the movable contact conductive arm and the straight portion of the line side terminal, tends to negate or cancel the repelling electromagnetic fields generated within the conducting paths of the stationary contact and movable contact conductive arm.